1. Field of the Invention
This invention relates to a fluorescent display device, and more particularly to a fluorescent display device capable of reducing grid control voltage and current to be driven directly by a MOSIC or a LSI and performing high-density luminous display of the dot-matrix type.
2. Description of the Prior Art
There has been known a fluorescent display device which is adapted to perform luminous display by impinging electrons emitted from a filamentary cathode on an anode having a fluorescent layer deposited on the upper surface thereof and having anode potential selectively applied thereto. Such fluorescent display device has several advantages in use that luminous display easy to observe can be provided at a low voltage, it can be driven directly by a LSI due to its low power consumption, display of various luminous colors can be performed using fluorescent materials emitting different luminous lights, and the like. Thus, the fluorescent display device of such type has been extensively used for a display system in various types of electronic and electrical devices.
Recently, a fluorescent display device is desired to perform luminous displays in the form of figures and images as well as numerals and characters. It is also desired to accomplish high-density luminous display to improve the denseness of display.
In order to meet with such requirements, a dot-matrix type fluorescent display device has been developed and put into practical use which is constructed in a manner such that a plurality of micro anodes each having a fluorescent material of a rectangle or circular shape deposited thereon are arranged in a two-dimensional shape and are driven in a matrix mode. More particularly, such dot-matrix type fluorescent display device, as shown in FIGS. 1A and 1B, includes a substrate 4, a plurality of stripe-shaped anode conductors 1 provided on the substrate 4, fluorescent layers 2 deposited on each of the anode conductors 1 so that each fluorescent layer 2 forms a single picture cell, a plurality of mesh-like control electrodes 3 arranged above the fluorescent layers 2 in the direction across the anode conductors 1 so as to oppose to the fluorescent layers. In the dot-matrix type fluorescent display device constructed in such manner, when electrons e emitted from a cathode (not shown) impinge on the fluorescent layers 2 positioned at the intersections between the anode conductors and the control electrodes to which anode voltage and control voltage are respectively applied, luminous display in the form of numerals, figures or the like is effected by a combination of the fluorescent layers emitting lights.
As seen from the foregoing, the dot-matrix type fluorescent display device is adapted to form a matrix using the anode conductors and control electrodes and excite each of the fluorescent layers 2 positioned at the intersections between the both electrodes with electrons emitted from the cathode to allow it to emit light.
In order to improve the density of luminous display obtained by a fluorescent display device of such type, it is required to arrange the anode conductors one after another at narrow intervals as shown in FIG. 1B. This results in the control electrodes 3 being required to be arranged at narrow intervals. However, such arrangement of control electrodes at narrow intervals causes an electric field generated by the adjacent control electrodes to adversely affect a passage through which electrons impinge on the fluorescent layers, this resulting in light emitting fluorescent layers 2 having non-light emitting regions or display-defect regions.
In view of such disadvantage, the inventors previously developed a fluorescent display device as shown in FIGS. 2A and 2B. The fluorescent display device includes a fluorescent display tube section comprising a substrate 11 made of an insulating material, a plurality of anode conductors 12 disposed in parallel with each other on the substrate each having a fluorescent layer 14 deposited thereon, a plurality of control electrodes 15 arranged through spacers 16 above the anode conductors each extending in the direction across the anode conductors and cathodes 17 stretched above the control electrodes, wherein each region on the anode conductors 12 controlled by each adjacent two control electrodes define one picture cell. The fluorescent display device further includes a driving circuit section (not shown) which acts to simultaneously apply a control voltage to each adjacent two control electrodes 15. In the fluorescent display device, the picture cells are defined by regions on the anode conductors controlled by the respective adjacent two control electrodes and luminous displays is obtained by simultaneously applying a control voltage to each adjacent two control electrodes 15 to allow the corresponding picture cell to emit light.
Thus, in the fluorescent display device, it is possible to use wires of a micro diameter or width as the control electrodes 15 to allow the picture cells to be arranged at narrow intervals, to thereby effect luminous display of a high-density. In addition, the fluorescent display device is adapted to simultaneously apply a control voltage to each adjacent two control electrodes, therefore, it has another advantage of preventing display defects and producing a high-density luminous display in the form of characters, figures or the like with high quality and clearness, because a passage of impinging electrons on the fluorescent layer is not affected by electric field of unselected control electrodes.
Recently, it has been desired that such fluorescent display device has a fluorescent display tube provided therein with picture cells of 128 or 256 in number disposed in parallel on one anode conductor 12 in order to accomplish luminous display of a higher density. However, the provision of such large number of picture cells causes the fluorescent display device to have an unsufficient duty factor. Supposing that anode voltage and control voltage are constant; the smaller the duty factor is, the more the luminance of display decreases. This means that it is required to increase anode voltage and control voltage in order to obtain display of a sufficient luminance. However, this results in a power consumption of the control electrodes substantially increasing to deform the control electrodes due to temperature rise thereof, so that the fluorescent display device decreases in reliability in operation. Further, the fluorescent display device is adapted to be driven through the anodes and control electrodes. However, this requires to increase driving voltages such as anode voltage and control voltage, so that it is impossible to drive the fluorescent display device by means of a MOSIC, a LSI or the like. This causes the structure of the driving circuit to be complicated, the display device to be decreased in reliability and the manufacturing cost of the device to be increased.
Furthermore, there has been a further need for a fluorescent display device capable of obtaining a luminous display of multi-colors as well as of a high-density. A conventional fluorescent display device performing such multi-color luminous display is generally constructed in such a manner as shown in FIG. 3, which is a plan view showing the essential portion of such fluorescent display device. More particularly, the fluorescent display device has a fluorescent display tube including a plurality of anode conductors 12b, 12g, 12r, 13b . . . arranged in parallel at predetermined intervals on a substrate, the anode conductors having fluorescent materials of different luminous colors deposited thereon, respectively. In the fluorescent display device illustrated, the anode conductors 12b, 12g and 12r respectively have fluorescent materials of blue, green and red luminous colors B, G and R intermittently deposited thereon. The anode conductor 13B has a fluorescent material of a blue luminous color deposited thereon, and further, fluorescent materials of green and red luminous colors are repeatedly provided in the same manner. Above the fluorescent layers, a plurality of mesh-like control electrodes 3 are arranged in the direction perpendicular to the anode conductors so as to cover the respective rays of the fluorescent materials formed in the longitudinal direction. The fluorescent display device further includes lead-out wires (not shown) for leading the respective anode conductors 12b, 12g, 12r, 13b . . . to the outside of the fluorescent display tube and lead-out wires (not shown) for the control electrodes. The fluorescent display tube is adapted to perform luminous display by selectively applying display signals to the anode conductors and control electrodes and impinging electrons emitted from a cathode (not shown) on the fluorescent materials positioned at the intersections between the selected anode conductors and control electrodes.
However, the fluorescent display device of such type has a fatal disadvantage of requiring a numerous number of lead-out wires, to thereby complicate the wiring and the connection of the lead-out wires to external terminals.
More particularly, when a alternately obtaining luminous displays in three colors of blue, green and red, one picture cell must be formed by three fluorescent materials B, G and R arranged in the longitudinal direction. This requires anode conductors in number three times picture cells arranged in the longitudinal direction. For example, when the number of picture cells arranged in the longitudinal direction is 128 or 256, it is necessary to provide anode conductors of 384 or 768 in number. This requires a numerous number of lead-out wires and causes the connection of wires to external terminals to be complicated.
In addition, the provision of such high number of anode conductors has another disadvantage of decreasing a duty factor, for example, when scanning time-divisionally the anode conductors to accomplish luminous display. As mentioned hereinbefore, supposing that anode voltage and control voltage are constant; the smaller the duty factor becomes, the more the luminance of display decreases. Thus, in order to keep the luminance of display at a satisfactory level, it is required to increase anode voltage and/or control voltage.
However, the increase in driving voltage results in a large amount of control current flowing into the control electrodes, to thereby cause the control electrodes to be deformed due to joule heat generated. Also, this renders the direct driving of the fluorescent display device by means of a MOSIC, a LSI or the like substantially impossible, resulting in the driving circuit being complicated in structure, the fluorescent display device being decreasing in reliability and the manufacturing cost being substantially increased.
Furthermore, the control electrodes used in the fluorescent display device are formed in a meshy shape. This causes the control electrodes to have a relatively large width, thus, it is impossible to arrange the picture cells at significantly narrow intervals.